Phase I studies: initial studies of toxicity of new drugs, new schedules of dosage or new combination of drugs. Phase II studies: non-randomized studies of the effectiveness of a specific treatment plan in a series of patients with specific diseases. Phase III studies: randomized comparisons (double-blind if feasible) of two or more treatment plans. Often comparison is made between a plan shown to be effective in a Phase II study and what is considered to be best standard treatment from previous studies. The majority of studies is directed against hematological malignancies, especially Hodgkin's disease, acute leukemia in adults, chronic lymphocytic leukemia and lymphomas. Emphasis is now shifting toward solid tumors. Phase I studies are done in patients with solid tumors and Phase II and III studies are being devised for solid tumors in which there is some evidence of effect. We deal primarily with chemotherapeutic drugs but are now incorporating the use of radiotherapy in comparison with chemotherapy or in combination with chemotherapy. Immunotherapeutic approaches are being explored. In addition to Group studies as described, ancillary studies at one or more institutions are encouraged. 1) Preliminary studies which may lead to data justifying a Group study. 2) Basic investigations directed toward elucidating mechanism of action or other aspects of treatment given in a Group protocol. 3) Studies directed at better methods of diagnosis or classification of diseases under study or better methods of evaluation of results. Emphasis is placed upon thorough planning, careful review of data and statistically sound evaluation of results. Important secondary benefits of these studies are the excellence of patient care and improved training of house officers and medical students.